An optically active carboxylic acid is attracting attention as an intermediate for synthesizing useful compounds, such as naturally-occurring physiologically active substances, or a liquid crystal material.
Knowing processes for asymmetric synthesis of an optically active carboxylic acid include (1) a process of using a naturally-occurring optically active substance, (2) a process of utilizing an asymmetric hydrogenation reaction using a microorganism, and (3) a process of asymmetric hydrogenation using a specific catalyst.
Among them, included in a process for obtaining an optically active carboxylic acid through asymmetric synthesis from an .alpha.,.beta.-unsaturated carboxylic acid is the process disclosed in JP-A-63-239245 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
The conventional techniques of asymmetric hydrogenation generally employ hydrogen gas as a source of hydrogen and hence require a pressure-resistant reactor for hydrogenation, e.g., an autoclave, and attachment equipment, such as a bomb or a pressure tank for feeding hydrogen gas. Thus, these processes involve difficulty in handling the equipment.